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PSU immediate shutdown troubleshooting help pls...

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December 21, 2010 2:15:59 AM

Couple of days ago I'm rendering some video and begin to smell something strange. Since one of my neighbors sometimes burns some "unusual" stuff in his fireplace, I went outside to see if it was outside or inside (wasn't out there). By the time I got back in the smell was getting pretty strong. As I was shutting my system down (normally - thru Win7) it shut itself down completely before windows could do it.

When I opened the case the smell was fairly strong there. So, while it's cooling down I took the time to clean all the fans & intakes - including the fins on my Artic Freezer 7 Pro Fluid cooler. Since it had been barely a year since I built the system I wasn't prepared to see how blocked the fins were in the Artic cooler (my bad). So I'm guessing fried cpu, but since I had it opened up I went ahead and checked my OCZ 700 PSU with my PSU tester and it showed only the 5v light. Hmmm...

So... I have a spare 750w PSU (that I know is good) and, using it, I plug in ONLY the main 24pin and 8pin 12v connectors and it would come on for half a sec and then shut down. So I pulled the CPU cooler and CPU itself and all the RAM, but results are the same. It would come on for half a sec and then shut down.

Here's my question(s):

1- I've never tried to "power up" a system board without a cpu installed, but would it (the PSU) normally keep running and the system board just complain about the missing CPU or would it try to power up and then immediatly shut down?

2- Before I buy another system board and or CPU are there any other checks I can do to pinpoint where the problem is?

Thx in advance for all input... :) 

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a c 156 V Motherboard
December 21, 2010 10:43:44 AM
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You need to install the CPU or nothing much will happen.

Work through our standard checklist and troubleshooting thread:
http://www.tomshardware.com/forum/261145-31-read-postin...
I mean work through, not just read over it. We spent a lot of time on this. It should find most of the problems.

If not, continue.

I have tested the following beep patterns on Gigabyte, eVGA, and ECS motherboards. Other BIOS' may be different.

Breadboard - that will help isolate any kind of case problem you might have.
http://www.tomshardware.com/forum/262730-31-breadboardi...

Breadboard with just motherboard, CPU & HSF, case speaker, and PSU.

Make sure you plug the CPU power cable in. The system will not boot without it.

I always breadboard a new build. It takes only a few minutes, and you know you are putting good parts in the case once you are finished.

You can turn on the PC by momentarily shorting the two pins that the case power switch goes to. You should hear a series of long, single beeps indicating memory problems. Silence indicates a problem with (in most likely order) the PSU, motherboard, or CPU. Remember, at this time, you do not have a graphics card installed so the load on your PSU will be reduced.

If no beeps:
Running fans and drives and motherboard LED's do not necessarily indicate a good PSU. In the absence of a single short beep, they also do not indicate that the system is booting.

At this point, you can sort of check the PSU. Try to borrow a known good PSU of around 550 - 600 watts. That will power just about any system with a single GPU. If you cannot do that, use a DMM to measure the voltages. Measure between the colored wires and either chassis ground or the black wires. Yellow wires should be 12 volts. Red wires: +5 volts, orange wires: +3.3 volts, blue wire : -12 volts, violet wire: 5 volts always on. Tolerances are +/- 5% except for the -12 volts which is +/- 10%.

The gray wire is really important. It should go from 0 to +5 volts when you turn the PSU on with the case switch. CPU needs this signal to boot.

You can turn on the PSU by completely disconnecting the PSU and using a paperclip or jumper wire to short the green wire to one of the neighboring black wires.
http://www.youtube.com/watch?v=5FWXgQSokF4&feature=yout...

A way that might be easier is to use the main power plug. Working from the back of the plug where the wires come out, use a bare paperclip to short between the green wire and one of the neighboring black wires. That will do the same thing with an installed PSU. It is also an easy way to bypass a questionable case power switch.

This checks the PSU under no load conditions, so it is not completely reliable. But if it can not pass this, it is dead. Then repeat the checks with the PSU plugged into the computer to put a load on the PSU.

If the system beeps:
If it looks like the PSU is good, install a memory stick. Boot. Beep pattern should change to one long and several short beeps indicating a missing graphics card.

Silence or long single beeps indicate a problem with the memory.

Insert the video card and connect any necessary PCIe power connectors. Boot. At this point, the system should POST successfully (a single short beep). Notice that you do not need keyboard, mouse, monitor, or drives to successfully POST.
At this point, if the system doesn't work, it's either the video card or an inadequate PSU. Or rarely - the motherboard's PCIe interface.

Now start connecting the rest of the devices starting with the monitor, then keyboard and mouse, then the rest of the devices, testing after each step. It's possible that you can pass the POST with a defective video card. The POST routines can only check the video interface. It cannot check the internal parts of the video card.
December 22, 2010 1:38:43 AM

jsc said:
You need to install the CPU or nothing much will happen.

Work through our standard checklist and troubleshooting thread:
http://www.tomshardware.com/forum/261145-31-read-postin...
I mean work through, not just read over it. We spent a lot of time on this. It should find most of the problems.

If not, continue.

I have tested the following beep patterns on Gigabyte, eVGA, and ECS motherboards. Other BIOS' may be different.

Breadboard - that will help isolate any kind of case problem you might have.
http://www.tomshardware.com/forum/262730-31-breadboardi...

Breadboard with just motherboard, CPU & HSF, case speaker, and PSU.

Make sure you plug the CPU power cable in. The system will not boot without it.

I always breadboard a new build. It takes only a few minutes, and you know you are putting good parts in the case once you are finished.

You can turn on the PC by momentarily shorting the two pins that the case power switch goes to. You should hear a series of long, single beeps indicating memory problems. Silence indicates a problem with (in most likely order) the PSU, motherboard, or CPU. Remember, at this time, you do not have a graphics card installed so the load on your PSU will be reduced.

If no beeps:
Running fans and drives and motherboard LED's do not necessarily indicate a good PSU. In the absence of a single short beep, they also do not indicate that the system is booting.

At this point, you can sort of check the PSU. Try to borrow a known good PSU of around 550 - 600 watts. That will power just about any system with a single GPU. If you cannot do that, use a DMM to measure the voltages. Measure between the colored wires and either chassis ground or the black wires. Yellow wires should be 12 volts. Red wires: +5 volts, orange wires: +3.3 volts, blue wire : -12 volts, violet wire: 5 volts always on. Tolerances are +/- 5% except for the -12 volts which is +/- 10%.

The gray wire is really important. It should go from 0 to +5 volts when you turn the PSU on with the case switch. CPU needs this signal to boot.

You can turn on the PSU by completely disconnecting the PSU and using a paperclip or jumper wire to short the green wire to one of the neighboring black wires.
http://www.youtube.com/watch?v=5FWXgQSokF4&feature=yout...

A way that might be easier is to use the main power plug. Working from the back of the plug where the wires come out, use a bare paperclip to short between the green wire and one of the neighboring black wires. That will do the same thing with an installed PSU. It is also an easy way to bypass a questionable case power switch.

This checks the PSU under no load conditions, so it is not completely reliable. But if it can not pass this, it is dead. Then repeat the checks with the PSU plugged into the computer to put a load on the PSU.

If the system beeps:
If it looks like the PSU is good, install a memory stick. Boot. Beep pattern should change to one long and several short beeps indicating a missing graphics card.

Silence or long single beeps indicate a problem with the memory.

Insert the video card and connect any necessary PCIe power connectors. Boot. At this point, the system should POST successfully (a single short beep). Notice that you do not need keyboard, mouse, monitor, or drives to successfully POST.
At this point, if the system doesn't work, it's either the video card or an inadequate PSU. Or rarely - the motherboard's PCIe interface.

Now start connecting the rest of the devices starting with the monitor, then keyboard and mouse, then the rest of the devices, testing after each step. It's possible that you can pass the POST with a defective video card. The POST routines can only check the video interface. It cannot check the internal parts of the video card.


I went thru the breadboard testing after cleaning the CPU of all old thermal compound (as well as the old compound on the CPU cooler) and re-connecting. Tried 2 different sticks of RAM. Tested the PSU with paperclip, tests fine.

The onboard LED's on the system board come on as soon as power is applied and then almost immediatly turn off. The PSU fan never even has enough time to begin to spin up before it all shuts down again.

I don't know whether to buy a new CPU or system board, and I hate the thought of buying one and finding out it's the other.

Isn't there some way to determine which of these are bad - without the ability to substitute another CPU?
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a c 156 V Motherboard
December 22, 2010 1:07:31 PM

Do you have a case speaker?

grindy said:

The onboard LED's on the system board come on as soon as power is applied and then almost immediatly turn off. The PSU fan never even has enough time to begin to spin up before it all shuts down again.

Does that happen with only CPU and PSU installed? Does that happen with both PSU's?

Unfortunately, at this point, about all you can do is test by substitution. After testing with two PSU's, the motherboard is likely to be the problem.
January 3, 2011 4:53:15 PM

Best answer selected by grindy.
!